1. Field of the Invention
The present invention relates to a keyboard for use in a word processor or computer, and relates in particular to a keyboard spill-proofing mechanism that prevents the inflow of water droplets, coffee or other liquids to a membrane sheet having an electrical circuit inside the keyboard.
2. Description of the Prior Art
A typical problem faced by keyboard users is that when a beverage such as coffee is spilled on a keyboard of a computer or word processor, the liquid reaches circuit boards with sensitive electronic components within the keyboard and results in short circuits or other electrical problems. In the past, sealing parts were positioned around circuit boards in the places where liquids could possibly enter the keyboard so that liquids would not reach the circuit boards or other sensitive components. In this keyboard design, the circuit boards were sealed by pressing and joining the sealing parts with a joining piece, etc. between the keyboard upper and lower covers, thus preventing the penetration of liquids to the circuit board.
As described above, placing the sealing parts around a circuit board and pressure joining the sealing parts to an upper cover and a lower cover may result in water tightness or spill proofing the circuit board. However, the sealing parts must be placed under a considerable amount of adhesion pressure in order to achieve the desired level of spill proofing. Accordingly, a disadvantage of this design is that to obtain rigidity sufficient to withstand the significant amount of the required adhesion pressure, the slab thickness of peripheral parts, etc. must be increased. An increased thickness of such parts results in a thicker keyboard. Another disadvantage of this design is that there is also a necessity to control accuracies in the assembly process in order attain the desired level of spill proofing obtained by adhesion pressure. Such increased production requirements result in a decline in work efficiency.
Another spill-proofing keyboard design is found in Laid Open Japanese Patent No. 2001-228950. This patent discloses a waterproof keyboard device equipped with a keyboard unit, an enclosure, and absorptive pieces. The enclosure is comprised of holders that hold the keyboard unit, and a housing that houses a printed circuit board. The absorptive pieces are placed around the holders to absorb liquids and to prevent spillage onto the circuit board. These absorptive pieces are comprised of a water-permeable surface sheet and a water-impermeable underside sheet. Additionally, an absorptive hydroscopic polymer is positioned between the surface and underside sheet of the absorptive pieces. A disadvantage of this design is that the structure of the absorptive pieces is complex and may result in increased production costs.